Safety mechanism for weight-set downhole tool

ABSTRACT

A safety trip button ( 12 ) is described for a weight-set downhole tool. The button operates between the tool body ( 36 ) and a sleeve ( 34 ) of the tool, locking them initially together. When the tool reaches a selected formation ( 44 ) in a well bore, the button engages the formation ( 44 ) which unlocks the body and sleeve. The button is kept in the unlocked position by virtue of the formation while the tool is set. The button prevents premature setting of the tool and finds application on weight set tools such as packers and circulation tools.

BACKGROUND OF THE INVENTION

The present invention relates to safety features in downhole tools andin particular to a safety trip button to prevent premature setting inweight set downhole tools.

A number of downhole tools as used in the oil and gas industry areoperated within a well bore by contacting or landing part of the toolonto a formation located within the well bore. Typically a sleeve of thetool is landed on a liner top PBR (polished bore receptacle), causingthe weight of the tool to force the tool into the liner while the sleeveremains stationary on the liner top. The relative movement of the sleeveon the tool body operates the tool, for example by opening radial portsor by compressing a packer.

In order that the sleeve does not move when the tool is inserted or runinto the well bore, shear pins are typically inserted between the toolbody and the sleeve to hold the sleeve in place. When the tool is landedon the liner top, the relative movement of the sleeve to the tool bodycauses the pins to shear thereby allowing operation of the tool.

A major disadvantage of these weight set tools is that they can beoperated by the sleeve contacting any formation in the well bore. Forexample if the sleeve comes into contact with debris adhering to thewalls of the casing or at a casing joint where the internal casingdiameters are mismatched, the sleeve may be jarred or stick at thatpoint in the well bore. Once stationary the tool body may be free tofall with a sufficient relative force to shear the pins. Thus the toolwill be activated and operate at the incorrect position in the wellbore.

It is an object of at least one embodiment of the present invention toprovide a safety mechanism to prevent premature setting of a weight settool in a well bore.

It is a further object of at least one embodiment of the presentinvention to provide a safety trip button which shears only when aweight set tool contacts a selected formation in a well bore.

It is a yet further object of at least one embodiment of the presentinvention to provide a compression set packer tool which includes asafety mechanism to prevent premature setting of the packer.

SUMMARY OF THE INVENTION

According to a first aspect of the present invention there is provided asafety mechanism for use in a weight set downhole tool to prevent thetool from setting before an operating element of the tool has landed ona selected formation in a well bore, the mechanism comprising a buttonmounted in a first position to lock the operating element to the toolbody, the button having a face engageable with the selected formation,whereupon engagement with the selected formation moves the button fromthe first position to a second position, disengaging the lock, andwherein the selected formation maintains the button in the secondposition while the selected formation contacts the operating elementthereby setting the tool.

As the tool cannot be set until the selected formation provides the dualrole of holding the button in the second position and contacting theoperating element, it is unlikely that any unintended formation in thewell bore could achieve this and thus the tool will not operate until itreaches the selected formation.

Preferably the button comprises a cylindrical body which is mountedthrough a portion of the operating element and a portion of the toolbody to lock each together. Locking prevents the operating element frommoving in relation to the tool body so that the tool can be run into thewell bore.

Preferably also the safety mechanism includes retaining means to holdthe button to the operating portion and the tool body once the tool isset. The retaining means may be one or more bissell pins. The one ormore bissell pins may be shearable. The retaining means may be a magnet,the magnet being mounted on a surface to attract another surface andhold the two surfaces together.

Preferably the face of the button is held proud of the tool in the firstposition. Preferably the surface is located facing the selectedformation. More preferably the face is a plane surface located at anacute angle to the tool in the first position. Thus as the formationrides past the face it forces the button towards the tool into thesecond position.

More preferably the button includes a shearable section. The shearablesection may be a narrower portion of the button, a portion of the buttonmade of a differing material or a combination thereof. When the buttonis in the second position the lock is disengaged by the movement of theshearable section to a position where it may be sheared.

In a preferred embodiment the operating element is a sleeve and theselected formation is a polished bore receptacle.

According to a second aspect of the present invention there is provideda weight set downhole tool, the tool including a tool body mountable ona work string, an operating element slidably mounted on the tool bodywhich operates the tool by contacting a formation in a well bore,shearable retaining means to hold the operating element to the tool bodyuntil such time as adequate force is applied to shear the retainingmeans, and a safety mechanism to prevent shearing of the retaining meansuntil the operating element has contacted a selected formation.

Preferably the operating element is a sleeve.

Preferably the shearable retaining means is one or more shear pins.

Preferably the selected formation is a polished bore receptacle.

Preferably the safety mechanism is according to the first aspect.

Preferably the downhole tool is a circulation tool. Preferably also thedownhole tool may be a packer tool.

Preferably the downhole tool further comprises an integral bypass meansto allow fluid to pass through the tool as it is run into the well bore.More preferably the bypass means are ports or channels. The bypass meansmay by opened or closed by virtue of the movement of the operatingelement when the tool is set.

Preferably also the downhole tool includes cleaning means. The cleaningmeans may be brushes, scrapers or milling elements. Preferably thecleaning means are mounted below the operating element so that theyreach the formation prior to the operating means. Alternatively thecleaning means may be located on the operating element so that unwantedformations such as debris can be removed before contacting the safetymechanism.

According to a third aspect of the present invention there is provided amethod of preventing a weight set downhole tool setting prematurelybefore an operating element of the tool has landed on a selectedformation, the method comprising the steps:

(a) running a weight set downhole tool including a safety mechanism intoa well bore on a work string;

(b) engaging a face of the safety mechanism on to the selected formationto move the safety mechanism to a released position; and

(c) engaging the operating element on to the selected formation to setthe tool while the selected formation maintains the safety mechanism inthe released position.

Preferably the method includes the step of shearing the safety mechanismwhen the tool is set.

BRIEF DESCRIPTION OF THE DRAWINGS

An embodiment of the present invention will now be described by way ofexample only with reference to the following drawings of which:

FIG. 1 is a schematic cross sectional view through a downhole toolincluding a safety mechanism in accordance with a preferred embodimentof the present invention;

FIG. 2 is a schematic cross sectional view through section A–A′ of FIG.1;

FIG. 3 is a schematic cross sectional view of the tool of FIG. 1 in theset position; and

FIG. 4 is a schematic cross sectional view of a packer tool including asafety mechanism in accordance with the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference is initially made to FIG. 1 of the drawings which illustratesa safety mechanism, generally indicated by reference numeral 10, inaccordance with a preferred embodiment of the present invention. Safetymechanism 10 comprises a cylindrical body or button 12. On one end 14 ofthe button 12 there is a contact face 16. Face 16 is planar and locatedat an acute angle to the button 12. At the opposing end 18 there islocated a magnet 20. Located between opposing ends 14,18 is a narrowedsection 22 of the button 12. The narrowed section provides a weak pointon the button 12 making it susceptible to shearing across the narrowsection 22. It will be appreciated that instead of a narrow section thebutton could include a section of differing material which is weakerthan the remaining material and be equally susceptible to shearing.

Further features of the button 12 can be seen with the aid of FIG. 2.Through the button 12 is located a channel 24 at each end of which areinserted bissell pins 26,28. At one end of the channel 24 there is anopening 30 wide enough to clear the bissell pin 28. No such opening islocated at the other end of the channel 24. Located at end 14 there isan aperture 32. Aperture 32 includes a screw thread such that the buttonmay be removed by insertion of a mating screw into the aperture 32.

In use, the button 12 is inserted through a portion of a sleeve 34 and atool body 36, to which the sleeve 34 is located on. The bissel pins 26,28 locate into the sleeve 34 such that the narrow section 22 is keptaway from the shear plane 38 located between the sleeve 34 and the toolbody 36.

When the tool is inserted in a well bore (not shown) the sleeve 34 maycome into contact with any irregularities or protrusions from the wallsof the well bore. For instance debris or cuttings may adhere to walls ofa casing while joints in the casing or liner may be mismatched leavingledges. On contacting these formations the sleeve 34 may stick or becomejarred. Once stationary the weight bearing down on the tool body 36 willcause a force to exist between the sleeve 34 and the tool body 36 alongthe shear plane 38. Ordinarily this force may be sufficient to cause thestandard shear pins 42, retaining the sleeve 34 to the tool body 36, toshear and as a result the tool would set at that point in the well bore.However, with the safety mechanism 10 in the position shown in FIG. 1,the first position, the sleeve 34 and tool body 36 are prevented fromshearing apart by virtue of the section 40 of the button 12 lying acrossthe shear plane 38. Thus premature setting of the tool is avoided.

When the tool reaches a selected formation 44, in this case a polishedbore receptacle (PBR) on a liner top, upper surface 46 of the PBR 44will engage with the contact face 16 of the button 12. As the tool movesinto the liner the face 16 and surface 44 will ride over each other withthe result that the button 12 will be pushed in towards a recess 48 inthe tool body 36. The force exerted by the PBR 44 on the button 12 issufficient to break a first bissell pin 26. The opening 30 around thesecond bissell pin 28 allows the button to shift from a first position,sitting proud of the sleeve 34, to a second position within recess 48,while still retaining the button 12 to the sleeve 34.

In the second position, the magnet 20 is located in the base of therecess 48 and the narrow section 22 lies on the shear plane 38. Thebutton 12 is held in this position by the surface 50 of the PBR 44. Thisis illustrated in FIG. 3 where the tool has moved further into the wellbore such that the surface 46 of the PBR 44 has contacted a surface 52of the sleeve 34. Further this contact has caused the sleeve 34 toremain stationary relative to the tool body 36. Weight applied to thetool body 36 now causes the shear pins 42 to shear along with the narrowsection 22 of the safety mechanism 10. Once sheared the sleeve 34 movesrelative to the tool body 36 to set the tool as shown in the Figure.While the tool is being set the button 12 is always held in the secondposition, where it may be sheared, by the continued contact of thesurface 50 of the PBR 44 with the face 16 of the button 12. Thus thedual function of the PBR 44 in both holding the button 12 in the secondposition while contacting the sleeve 34 to set the tool allows the toolonly to be set by the PBR 44.

Once the button 12 has been sheared when the tool is set, the secondbissell pin 28 holds the upper section 54 of the button 12 to the sleeve34 to prevent it from becoming free and lodging somewhere in the toolwhere it may cause damage. Similarly, magnet 20 holds the lower section40 of the sheared button 12 in the recess 48 against the tool body 36and prevents it from interfering with the operation of the tool.

When the tool is retrieved, the button 12 may be removed from the sleeve34 by inserting a screw into the aperture 32 and withdrawing the button12. The lower section 40 may be removed via a magnet or by simplypulling on the remains of the narrow section 22.

Reference is now made to FIG. 4 of the drawings which illustrates apacker tool, generally indicated by reference numeral 100, in accordancewith an embodiment of the present invention. In FIG. 4 like parts tothose of the other Figures have been given the same reference numeralwith the addition of 100.

Packer tool 100 comprises a one piece full strength drill pipe mandrel60, making up the tool body 136, and having a longitudinal bore 62therethrough. A box section 64 connection is located at a top end of themandrel 60 and a threaded pin section 66 is located at a bottom end ofthe mandrel 60. Sections 64,66 provide for connection of the packer tool100 to upper and lower sections of a drill pipe (not shown).

Mounted on the mandrel 60 is a compression set packer 68 with integralby pass means 70 which will be described hereinafter with regard tooperation of the tool 100.

Below the packer 68 is a stabiliser sleeve 72. Sleeve 72 is rotatablewith respect to the mandrel 60. Raised portions or blades 74 provide a‘stand off’ for the tool 100 from the walls of the well bore and lowertorque on the tool 100 during insertion into the well bore.

Located below the stabiliser sleeve 72 is a Razor Back Lantern (TradeMark) 76. The Lantern 76 provides a set of scrapers for cleaning thewell bore prior to setting the packer 68. Though scrapers are shown itwill be appreciated that the scrapers could be replaced by brushes orother suitable cleaning means.

The safety mechanism 110 and the contact surface 152 of the sleeve 134are located on a top dress mill 78 at a lower end of the tool 100. Thetop dress mill 78 can be used to dress off the PBR (not shown) top ifrequired, while a section 80 of the top dress mill 78 can be used toclean the inside walls of the PBR.

The tool 100 operates as described hereinbefore with reference to FIGS.1 to 3. When run in the bypass means 70 is open allowing fluid to flowaround, behind the packer and thus reduce the amount of debriscontacting the packer outer surface 82. Setting down a weight ofapproximately 12,000 lbs will cause the sleeve 134 to engage with thePBR and the safety mechanism 110 and the shear pins 142 to shear. A‘shear shudder’ will be felt on the drill string at the surface.Additionally the sleeve 134 will move across the bypass channel aroundthe packer and it will be closed off. At the same time the sleevecontacts the base of the packer 68. The upper end of the packer is fixedto the tool body 136. Setting down further weight on the tool 100,typically 20,000 lbs of applied weight, forces the base of the packeragainst the sleeve 134 which causes the packer to be compressed and as aresult the rubber material of the packer 68 is compressed axially whileexpanding radially. Thus the packer 68 expands until the outer surface82 meets and seals against the wall of the well bore or casing, if used.The packer is therefore set. Additionally the packer 68 can be unset bymerely lifting the tool off the PBR whereupon the sleeve will fall backto its original position thereby releasing the packer 68 and opening thebypass means 70.

The principle advantage of the present invention is that it preventspremature setting of a weight set downhole tool before the tool haslanded on the selected formation.

A further advantage of the present invention is that it provides afailsafe compression set packer tool which allows an inflow or negativetest to be carried out on a liner over-lap and the liner shoe-track onthe same trip as the well bore clean-up. The tool further eliminates theneed for a controlled displacement of the whole well to lighter densityfluid through use of the retrievable packer to perform the test.

Modifications may be made to the embodiments described herein withoutdeparting from the scope thereof.

1. A safety mechanism for use in a weight set downhole tool to preventthe tool from setting before an operating element of the tool has landedon a selected formation in a well bore, the mechanism comprising abutton mounted in a first position to lock the operating element to thetool body, the button having a face engageable with the selectedformation, whereupon engagement with the selected formation moves thebutton from the first position to a second position, disengaging thelock, and wherein the button is maintained in the second position by theselected formation while the operating element contacts the selectedformation thereby setting the tool.
 2. A safety mechanism as claimed inclaim 1 wherein the button comprises a body which is mounted through aportion of the operating element and a portion of the tool body to lockeach together.
 3. A safety mechanism as claimed in claim 2 wherein thebody of the button is substantially cylindrical.
 4. A safety mechanismas claimed in claim 1 wherein the safety mechanism further includesretaining means to hold the button to the tool once the tool is set. 5.A safety mechanism as claimed in claim 4 wherein the retaining meanscomprises one or more bissell pins.
 6. A safety mechanism as claimed inclaim 4 wherein the retaining means comprises a magnet, the magnet beingmounted on a surface to attract another surface and hold the twosurfaces together.
 7. A safety mechanism as claimed in claim 1 whereinthe face of the button is held standing out from the tool in the firstposition.
 8. A safety mechanism as claimed in claim 7 wherein the faceis located facing the selected formation to engage the selectedformation.
 9. A safety mechanism as claimed in claim 7 wherein the faceis a plane surface located at an acute angle to the tool in the firstposition.
 10. A safety mechanism as claimed in claim 1 wherein thebutton includes a shearable portion.
 11. A weight set downhole tool, thetool including a tool body mountable on a work string, an operatingelement slidably mounted on the tool body which operates the tool bycontacting a formation in a well bore, shearable retaining means to holdthe operating element to the tool body until such time as adequate forceis applied to shear the retaining means, and a safety mechanism toprevent shearing of the retaining means until the operating element hascontacted a selected formation.
 12. A weight set downhole tool asclaimed in claim 11 wherein the operating element is a sleeve.
 13. Aweight set downhole tool as claimed in claim 11 wherein the shearableretaining means is one or more shear pins.
 14. A weight set downholetool as claimed in claim 11 wherein the selected formation is a polishedbore receptacle.
 15. A weight set downhole tool as claimed in claim 11wherein the safety mechanism is according to claim
 1. 16. A weight setdownhole tool as claimed in claim 11 wherein the downhole tool is acirculation tool.
 17. A weight set downhole tool as claimed in claim 11wherein the downhole tool is a packer tool.
 18. A weight set downholetool as claimed in claim 11 further comprising an integral bypass meansto allow fluid to pass through the tool as it is run into the well bore.19. A weight set downhole tool as claimed in claim 18 wherein the bypassmeans are ports or channels.
 20. A weight set downhole tool as claimedin claim 18 wherein the bypass means are opened or closed by virtue ofthe movement of the operating element when the tool is set.
 21. A weightset downhole tool as claimed in claim 11 wherein the downhole toolfurther includes cleaning means.
 22. A weight set downhole tool asclaimed in claim 21 wherein the cleaning means comprises brushes,scrapers or milling elements.
 23. A weight set downhole tool as claimedin claim 21 wherein the cleaning means are mounted below the operatingelement.
 24. A weight set downhole tool as claimed in claim 21 whereinthe cleaning means are located on the operating element.
 25. A method ofpreventing a weight set downhole tool setting prematurely before anoperating element of the tool has landed on a selected formation, themethod comprising the steps: a) running a weight set downhole toolincluding a safety mechanism into a well bore on a work string; b)engaging a face of the safety mechanism on to the selected formation tomove the safety mechanism to a released position; and c) engaging theoperating element on to the selected formation to set the tool while theselected formation maintains the safety mechanism in the releasedposition.
 26. A method as claimed in claim 25 further including the stepof shearing the safety mechanism when the tool is set.
 27. A method asclaimed in claim 25, wherein: the step of running the downhole tool intothe well bore comprises running the tool with a button of the safetymechanism mounted in a first position where the button locks theoperating element to a body of the tool; and wherein the step ofengaging the face of the safety mechanism on the selected formationcomprises engaging a face of the button with the selected formation,which moves the button from the first position to a second position,thereby disengaging the lock and moving the safety mechanism to thereleased position; and further wherein the step of engaging theoperating element on to the selected formation maintains the button inthe second position to maintain the safety mechanism in the releasedposition.
 28. A safety mechanism for use in a weight set downhole toolto prevent the tool from setting before an operating element of the toolhas landed on a selected formation in a well bore, the mechanismcomprising a button, the button comprising a substantially cylindricalbody mounted in a first position in which the button is mounted througha portion of the operating element and a portion of the tool body tolock the operating element to the tool body, and wherein the button hasa face engageable with the selected formation, whereupon engagement withthe selected formation moves the button from the first position to asecond position, disengaging the lock, and wherein the button ismaintained in the second position by the selected formation while theoperating element contacts the selected formation thereby setting thetool.
 29. A safety mechanism for use in a weight set downhole tool toprevent the tool from setting before an operating element of the toolhas landed on a selected formation in a well bore, the mechanismcomprising: a button mounted in a first position to lock the operatingelement to the tool body, the button having a face engageable with theselected formation, whereupon engagement with the selected formationmoves the button from the first position to a second position,disengaging the lock, and wherein the button is maintained in the secondposition by the selected formation while the operating element contactsthe selected formation thereby setting the tool; and a magnet to holdthe button to the tool once the tool is set, the magnet being mounted ona surface to attract another surface and hold the two surfaces together.30. A safety mechanism for use in a weight set downhole tool to preventthe tool from setting before an operating element of the tool has landedon a selected formation in a well bore, the mechanism comprising abutton mounted in a first position to lock the operating element to thetool body, the button having a face engageable with the selectedformation and a shearable portion, whereupon engagement with theselected formation moves the button from the first position to a secondposition, disengaging the lock, and wherein the button is maintained inthe second position by the selected formation while the operatingelement contacts the selected formation thereby setting the tool.
 31. Amethod of preventing a weight set downhole tool setting prematurelybefore an operating element of the tool has landed on a selectedformation, the method comprising the steps: a) running a weight setdownhole tool including a safety mechanism into a well bore on a workstring; b) engaging a face of the safety mechanism on to the selectedformation to move the safety mechanism to a released position; c)engaging the operating element on to the selected formation to set thetool while the selected formation maintains the safety mechanism in thereleased position; and d) shearing the safety mechanism when the tool isset.